We have investigated the mechanisms underlying the interactions between microtubules and clatharin coated vesicles (coated vesicle). We have chosen this organelle because preliminary studies in our laboratory have shown morphological connections between coated vesicles and microtubules in cultured fibroblasts in preparations of in vitro assembled microtubules, and in preparations of isolated intact microtubles from whole brain. Results from other laboratories have shown that coated vesicles are composed of a membrane vesicle which is enclosed by a basket composed principally of the protein clatharin. These vesicles appear to be involved in the transport of materials within cells as well as the recycling of membrane components at the end of nerves. Since interactions between the coated vesicles and microtubules have been observed both in situ and in vitro, our initial experiments have been directed toward developing assays to study the in vitro associations between microtubules and coated vesicles in order to understand how the interactions might be made and regulated in vivo. Preliminary results have demonstrated that we can assay binding of coated vesicles to microtubules in vitro using both negative stain and thin section electron microscopy and by several centrifugation techniques. While these assays are still being developed, we have shown that the coated vesicles bind to microtubules and that high molecular weight microtubule associated proteins (MAPs) are necessary for the binding. Microtubules assembled in the absence of MAPs do not have the ability to bind coated vesicles under the conditions of our assays.